Increasingly stringent evaporative fuel standards for automobiles and trucks demand that the fuel system component minimize the emission of fuel vapors through automotive components such as the fuel tank, fuel filler lines, fuel injector seals, and fuel seals. Elastomers employed in fuel seal applications generally require low temperature properties, e.g. glass transition temperature (Tg)<−20° C. to maintain sealing performance for cold weather. Various types of fluoroelastomers for fuel seals have been proposed to address these concerns. In general, the most successful of the elastomers generally contain perfluoromethylvinylether (PMVE). PMVE reduces the glass transition temperature but generally has an adverse effect upon permeation. Materials with the combination of improved low temperature sealing and better permeation resistant materials are needed to meet the regulations, which has consistently been moving toward zero fuel emission.
Because of the expense of the fluoroelastomer, especially PMVE monomer, it is often desirable to use an extender compounded with the fluoroelastomer. However, compared to other hydrocarbon elastomers, fluoroelastomer combined with a low loading filler provides an unusually high durometer. Thus rendering the compound ineffective for sealing applications.
Those skilled in the art of fluoroelastomers recognize that it is difficult to get low temperature performance while maintaining good permeation resistance. It would be an advantage to improve the fuel permeation rate of an elastomer while retaining low temperature performance.